Band pass filters and band stop filters are conventional passive elements for filtering microwave signals. Such elements are used to cut spurious wave and noise components in measurement instruments such as spectrum analyzers and amplifiers. Besides such elements are also utilized for improving the communication performance in a communication device such as a cellular phone.
In addition, in order to make a filtering frequency band variable, the filtering frequency is conventionally controlled with a combination of microwave transmission lines and semiconductor diodes by applying a voltage. Further, a method of using ferroelectric material for a transmission line base material to control the filtering frequency by applying a voltage to the ferroelectric material has been also reported.
Further, in order to selectively transmit only a signal of a certain frequency, a high performance microwave filter that generates a narrow pass band in a wide stop band is also devised.
Referring to the foregoing, Japanese Laid-Open Patent Application No. Heisei 03-108192 discloses an invention directed to a ferroelectric memory.
The ferroelectric memory of Japanese Laid-Open Patent Application No. Heisei 03-108192 is provided with a lower electrode, an upper electrode, a ferroelectric layer, and an antiferroelectric layer. The lower electrode is formed in the stripe shape. The upper electrode is arranged so as to be perpendicular to the lower electrode, and is also formed in the stripe shape. The ferroelectric layer is arranged between the lower electrode and the upper electrode, and changes the polarization state by the electric field applied between the both electrodes. The antiferroelectric layer is arranged between the lower electrode and the ferroelectric layer and/or between the upper electrode and the ferroelectric layer.
In addition, Japanese Laid-Open Utility Model Application No. Heisei 03-71598 discloses an invention directed to an electroluminescence light.
The electroluminescence light disclosed in Japanese Laid-Open Utility Model Application No. Heisei 03-71598 has an insulating layer and a light-emitting layer interleaved between a transparent electrode and a back electrode. Barium titaniate zirconate is employed for the insulating layer formed by dispersing high dielectric material powders in a binder.
Further, Japanese Laid-Open Patent Application No. Heisei 07-111407 discloses an invention directed to a ferroelectric transmission line.
The ferroelectric transmission line of Japanese Laid-Open Patent Application No. Heisei 07-111407 is provided with ferroelectric material on a ground conductor, the ferroelectric material having a variable dielectric constant which depends on the magnitude of an applied electric field. In addition, a transmission line through which microwave is propagated is formed by a conductor pattern on the ferroelectric material. By varying the dielectric constant of the ferroelectric material with a voltage applied to the conductor pattern, characteristics of the microwave are changed.
In addition, Japanese Laid-Open Patent Application No. Heisei 10-39265 discloses an invention directed to an electro-optic element.
The electro-optical element of Japanese Laid-Open Patent Application No. Heisei 10-39265 is provided with a ferroelectric substrate and polarization inversion domains formed within the ferroelectric substrate in a predetermined shape. At least one of the domain walls of the polarization inversion domains is perpendicular or approximately perpendicular to the main surface of the ferroelectric substrate. A light beam is formed so that the light beam passes at least two domain walls, and electrodes are disposed on the side surfaces of the ferroelectric substrate along the propagation direction of the light beam, which side surfaces are different from the main surface.
Further, Japanese Laid-Open Patent Application No. Heisei 11-239002 discloses an invention directed to a phase shifter. The phase shifter of Japanese Laid-Open Patent Application No. Heisei 11-239002 is capable of controlling a phase delay quantity in delaying the phase of the electromagnetic wave of 1 THz or less. This phase shifter is provided with a pair of transmission lines and dielectric material. In this case, the paired transmission lines, which are disposed so as to be opposed with each other, transmit the electromagnetic wave, and a control voltage of a frequency lower than that of the electromagnetic wave is applied between one transmission line and other transmission line for controlling the shift delay quantity. The dielectric material is provided between the paired transmission lines, and the dielectric constant thereof is varied in accordance with the control voltage. In addition, Japanese Laid-Open Patent Application No. 2006-60112 discloses an invention directed to a print circuit.
The print circuit of Japanese Laid-Open Patent Application No. 2006-60112 is provided with a transmission line having dielectric material body including ferroelectric material between a signal line and a ground or a power source line.
In addition, Japanese Laid-Open Patent Application No. 2006-145726 discloses an invention directed to an electromagnetic wave direction control element.
The electromagnetic wave direction control element of Japanese Laid-Open Patent Application No. 2006-145726 is formed with photonic crystal dielectric compound substance, high-dielectric constant dielectric substance, and low-dielectric constant dielectric substance. Here, the photonic crystal dielectric compound substance has a periodic structure such that second dielectric substance having a second dielectric constant is periodically arrayed in first dielectric substance having a first dielectric constant, of which second dielectric constant is different from the first dielectric constant. The high-dielectric constant dielectric substance has no periodic structure but has a third dielectric constant. The low-dielectric constant dielectric substance has no periodic structure but has a forth dielectric constant lower than the third dielectric constant. In addition, an input side photonic crystal portion, an input side crystal defect portion, an intermediate photonic crystal portion, an output side crystal defect portion, and an output side photonic crystal portion are sequentially arranged from an input end side of the electromagnetic wave toward an output end side of the electromagnetic wave. Here, the input side photonic crystal portion includes a photonic crystal dielectric compound substance. The input side crystal defect portion includes the high-dielectric constant dielectric substance. The intermediate photonic crystal portion includes a photonic crystal dielectric compound substance. The output side crystal defect portion includes the low-dielectric constant dielectric substance. The output side photonic crystal portion includes a photonic crystal dielectric compound substance.